There is a need in many and diverse fields for a small yet powerful and efficient air power source, whether for providing air pressure or for providing vacuum. Fluid compressors with such capabilities are known. See, for example, Maniscalco U.S. Pat. No. 2,114,719, but which involves complicated valving arrangements making the compressor inordinately large and expensive for many applications. Laerdal U.S. Pat. No. 3,499,601 discloses a compressor utilizing a double action valve of relatively simple construction but which does not yield itself to ready convertibility. Other patents of interest in this regard are Pribonic U.S. Pat. Nos. 3,151,805, Kirkwood 899,541, Shoemaker 2,477,093, Kanuch 2,680,347, Courtois 1,889,640, Lawhead 1,295,529 and Miller Defensive Publication T883011, but each relates to a mechanism which is sufficiently complicated in construction and limited in its convertibility as to not provide a device applicable for many uses contemplated herein.
A number of the foregoing patent references disclose utilization of a Scotch-yoke type of mechanism. Over the years, such a mechanism has been a favorite with designers and engineers. Its advantages are simplicity, ease of assembly and low cost. Basically, a Scotch-yoke mechanism comprises a reciprocating shaft to which is secured a transverse yoke, in combination with eccentric means guided within the yoke and reciprocated by means of a crankpin connected to a flywheel, or counterweight. As the flywheel rotates, the crankpin slider carried by it is constrained to reciprocate within the transverse yoke resulting in conversion of the rotary motion of the flywheel to reciprocating motion of the yoke. Satisfactory methods for lubricating a Scotch-yoke mechanism have not entirely been resolved. In particular, with the type of compressor contemplated herein, it is important that the interior of the compressor be kept as clean as possible from lubrication spray. Therefore, the use of a common grease packing is inappropriate. A number of prior suggestions have been made and one could make particular reference to the Enders U.S. Pat. Nos. 3,033,312, 3,119,460 and 3,162,267. However, the type of Scotch-yoke utilized in the Enders patents involves the use of a channel member requiring a degree of tolerance which would be desirable to decrease so as to enable as inexpensive construction as possible. Accordingly, the methods proposed for lubrication by the Enders patents are not applicable to the type of mechanism which is proposed herein. Other patents of minor interest with regard to lubrication are Campbell U.S. Pat. Nos. 3,590,957 and Russell 1,640,375.
The present invention provides a compressor having opposed coaxial cylinders at opposite ends and which is constructed for ready conversion to operate as a vacuum compressor. Advantageously, the foregoing is accomplished with a compressor of only modest size having relatively few components, which is inexpensive in construction and which does not require close tolerances for excellent operation. In comparison to compressors of a similar size which usually have a maximum efficiency of 35-40%, compressors constructed in accordance with the present invention can attain a peak compressor efficiency of up to 60%. The compressor is useful in a wide variety of applications ranging from an auto tire inflator which can be plugged into a cigarette lighter, as the pressure source of a load leveling pressure adjustable shock absorber, as a vacuum pump, for high pressure systems through staging, as a paint sprayer, as a water tank pressurizer, as a medical respirator and nebulizer, in computers as an air power source for small air motors, for inflating air bags and air shocks and for any other system requiring positive air pressure at high efficiency.
More specifically, the compressor comprises a housing including side walls and end walls (head plates) and defining first and second end chambers adjacent the end walls. A pair of cylinders are formed in the housing inwardly adjacent the end chambers and an open region is defined between the cylinders. In a preferred form of the invention, a manifold channel connects an exhaust port (or inlet port for vacuum operation) with the opposite end chambers.
A valve plate is disposed in each end chamber, each plate having an inner surface carrying hermetic seals to close the outer end of the cylinder thereat. A free space is left between the outer surface of the plate and the end wall of the housing. The valve plate is formed with an orifice aligned with the cylinder for communicating the cylinder with the free space and a flap valve is carried on the valve plate for opening and closing the orifice. In accordance with a particular embodiment herein for enabling the aforementioned convertibility, the valve plate extends across the outer end of the channel connected to the exhaust port and the plate is formed with an orifice aligned with that channel end so as to enable communication with the free space in the end chamber.
A piston is disposed in each cylinder and each piston is formed with an orifice so as to provide communication between the central open region and the interior region of the cylinder adjacent the respective valve plate. A flap valve is disposed on each piston for opening and closing the piston orifice. A mechanism acting as a "piston rod" is located in the open region and connects the two pistons for reciprocal movement, and means are provided for reciprocating the "piston rod" as a part of a Scotch-yoke type mechanism as will be hereinafter referred-to. By reversing the direction of the valve plates and disposing the piston flap valves on opposite sides, one can convert from one mode of operation to another with great facility. A motor can be mounted to the housing so that the facing of the motor encloses the central open region. Depending upon the mode of operation, vents are opened into the central region and filtration means are disposed in the vents as well as in the channels leading to the exhaust port, so as to provide dust and lint-free air.
In accordance with another particular embodiment of the invention, a Scotch-yoke type of mechanism is provided in which slider and yoke have mating cylindrical surfaces. Such construction provides inherent self-alignment so as to permit lower tolerances in manufacture and in assembly. The slider is constructed of lubricant-impregnated sintered or other porous bronze. A lubricant-containing cross hole is provided and the crankpin bearing hole extends past the cross hole across the slider. For extra long life, during construction, a lubricant-containing wick material is disposed in the cross hole and across the bearing hole. With the slider in place in the yoke, when the crankpin is inserted into the bearing hole it severs the wick material from the cross hole and displaces the severed wick material to the end of the bearing hole, against the yoke. The result is the provision of additional lubrication for both the inside surface of the yoke as well as the crankpin. The wick lubrication acts in conjunction with the lubricant-impregnated bronze to provide a unique lubrication mechanism having extremely long lubrication life, beyond that provided by the bronze slider alone.